The essential parameter in the cheese-making industry is the coagulation time because it marks the end point of the enzymatic phase and the start point of the aggregation. Furthermore, it is used to evaluate the cutting time that characterizes the time at which curd is cut. This paper proposes a non-destructive ultrasonic pulse-echo to monitor in real-time the acoustic impedance of milk during cheese manufacturing in order to predict the coagulation time. The evolution of the acoustic impedance is going through two phases the enzymatic phase and the aggregation phase. The transition point between these two phases defines the milk coagulation time. Three rennet concentrations and three temperatures were considered in our experiments to study the effect of these factors on coagulating milk. The experimental results prove that our proposed method determines the coagulation time with efficiency, and it is more simple compared with our previous work in which the phase velocity was used to determine the milk coagulation time. (C) 2017 Elsevier Ltd. All rights reserved.